Method of making return bends



1932- T. F. BIRMINGHAM 1,891,898

METHOD OF MAKING RETURN BENDS Filed Dec. 22, 1930 IIIIIIIIIIIuIIuIIII/IJ INVENTOR BY @l/%LQ ATTORNEY Patented Dec. 27, 1932 UNITED STATES PATENT OFFICE THOMAS E. BIRMINGHAM, OF HAMMOND, INDIANA, ASSIGNOR TO THE SUPERHEATER COMPANY, OF NEW YORK, N. Y.

METHOD OF MAKING RETURN BENDS Application filed December 22, 1930.

This invention relates to the art of making return bends and more particularly to the method described in U. S. Patent 1,169,209. It has for its object an improvement in this method when applied to pipes below a certain gage.

The general process for manufacturing return bends according to this patent has gone into extensive use and is well known. It need, therefore, not be described in any great detail. The steps may be briefly summarized as follows:

The two pipes to be united by a return bend are clamped together by any appropriate means in the relative position they will occupy in the finished product. The portions adjacent to the ends which are to be connected by the return bend are heated to the proper welding heat in a furnace. They are then placed into a die which has two cylindrical spaces to accommodate them, the wall separating these two spaces being cut away for a certain distance from the outer end, that is the end opposite the pipes. A plunger having two prongs adapted to enter the two pipes is forced into the open end of the die and into the pipes by a suitable mechanism. The conformation of the dies and the plunger is such that in performing its stroke, the plunger splits the juxtaposed walls of the two pipes, forcing the portions adjacent to the split outward so that the edges of the one pipe abut forcibly against those of the other, such abutting resulting in a weld. This completes this portion of the process and the present invention relates to an improvement in this part of the process. To form a complete return bend the open end must subsequently be closed by some means. If the structure is to be used for some other purposes, the end may not be closed but may be left open. It may for instance be rounded and have a pipe length safe-ended to it. The present invention does not concern itself either with the closing of, or any other further operation on, the structure.

One of the uses to which return bends made by the process briefly outlined above has been extensively applied is that of superheaters Serial No. 504,049.

for locomotives. In the manufacture of such superheaters the size of pipe commonly used in the past is one having an outside diameter of 1 the gage being #9. In the manufacture of such pipe it is impossible, however, to avoid accidental variations in the wall thickness. In purchasing pipe for the purpose above mentioned, #9 is the gage specified, but pipes whose wall thickness may run as'low as #10 or as high as #8 is accepted. The gages referred to are the Birmingham wire gage in which a wall thickness of gage #9 is 0.148, #8 being 0.165" and #10 being 0.134.

As has been found by many years experience that, with pipes within the limits stated, entirely satisfactory welds result from the process described above. Neither has any trouble been experienced with larger and heavier gage pipes. it was found in the past that greater difficulty was experienced when pipes of smaller outside diameter were used. The reason for this was not understood and a relatively large wastage from unsatisfactory welds was accepted as necessary. More recently, however, a design of locomotive superheater has come into general use in which a pipe of an outside diameter of 1%" is used. The difference between the former size of 1 outside diameter and the size just spoken of looks insufidcient to cause any particular difficulty. With the new size pipe the gage usually required for strength to resist the steam pressures is #11, that is, 0.120". Due to the variations in manufacture, however, the wall thickness of such #11 gage may run as low as #12, that is. 0.109. This, it will be noted, is almost .04 less than the average gage for the 1 pipe. It was finally suspected that this difference in wall thickness. although slight. was the real cause of the dificultv in obtaining goo-d welds. To obviate the difliculty, the present invention proposes to use pipes which are of heavier gage along the short portions at the ends which enter into the manufacture of the return bend, the gage of the remainder of the pipe being dictated bv considerations of strength only. The difficulty is thereby effectually removed. Whereas it had been suspected that the small outside diameter of the pipe caused the difficulty in welding, it was really the fact that the wall was too thin.

The invention is evidently not limited to pipes of small diameter. Where the pressures are low. even larger pipes need only thin walls to resist the pressures, and difficulty in making return bends will be encountered. By having the end portions of'hea-vier gage, the difficulty is removed.

It will be seen thatby the present invention a great saving results. 'Heretofore a heavier gage had to be used to form a satisfactory weld than was necessary for considerations of strength alone. By using the present invention a lighter gagepipe, determined entirely by considerations of strength, can be used, only the ends where the return bend is to be formed being of heavier gage.

lVhen superheater units or elements made according to the present invention are used in the usual form of locomotive superheater, a further advanta ge results. The units of such superheaters are arranged in flues, as is well known. If the heavier gage required for the best weld were used, the free gas area would be reduced throughout the length of the flue, with a resultant considerable resistance to the gas flow. VVith-units according to the present invention, the gas area is reduced over only a relatively very short distance, so that the flow is interfered with to only a small degree.

The invention will probably be entirely clear from the above but may be additionally discussed in connection with the accompanying drawing. In this drawing Fig. 1 shows two pipes of uniform gage as used heretofore held together ready for heating: Fig. 2 shows an end view of these pipes; Figs. 3 and 4 show views similar to 1 and 2 respectively, of the two pipes after the plunger has performed its stroke; Figs. 5 and 6 are views similar to Figs. 1 and 3 respectively, pipes according to the present invention being used; and Fig. 7 shows a completed return bend. with pipes according to the new method.

It will be noted that in Figs. 1 to 4, which represent the old practice, the gage of the pipes is uniform throughout. In the pipes shown in Fig. 5 the gage of the pipes, as at the points 1 is that determined by the internal pressure to which the finished procuct is to be exposed. This thickness in those cases to which the present application applies is too small to result in a good weld. The pipes, therefore, have a greater wall thickness, as at 2, over those portions where the return bend is to be made. It will be noted that the internal diameter is uniform throughout, the additional material all being on the outside. This is usually desirable in order that there may be no obstruction to the flow of the fluid circulating through the completed product, although it is not essentia In Fig. 6 the line along which the weld has been made is indicated by the dotted line 4;. This weld, it will be observed, is between wall portions of the thicker gage.

Fig. 7 shows a completed return bend, the end having been closed, as at 5, by any preferred method.

Iclaim:

1. The process of making a return bend with pipes whose wall thickness is sufficient to resist the stresses to which they will be exposed but insufficient to permit of the necessary welding, which comprises making. two pipes of v the wall-thickness required for strength except at the ends to be joined by return bends, said ends being thicker than re quired for strength and thick enough for welding, holding said pipes in the relative position they are to occupy in the finished product, heating the ends towelding heat, slitting the juxta-posed walls of the two pipes for a suitable distance from their ends, pressing portions adjacent to the slits outward and simultaneously causing them to abut in pairs and unite in a weld.

2. The process according to claim '1, the making of the pipes including making their internal diameter uniform throughout.

3. The process of uniting two pipes by a return bend or related structure comprising making two pipes of generally uniform gage except over those lengths where they are to be united, said lengths being of heavier gage,

slittingeachof said pipes inward from its end for a suitable distance along a line parallel to the axis, bending the portions adjacent to each slit outward into parallel planes, and welding the edges of said portions of one pipe to the corresponding edges of said portions of the other pipe.

7 THOMAS F. BIRMINGHAM. 

